When animals learn, they store their memories as anatomically distributed sets of circuit modifications. While such circuit modifications can be mapped with precision, and the biophysical and molecular mechanisms underlying each locus of plasticity can be worked out, it has proven very difficult to investigate the way that the information acquired in learning corresponds to these sites of circuit modification. The purpose of this project is to develop and apply a technique for doing this, involving the interactive use of electrophysiology and computer modeling. Since this approach is not yet feasible in vertebrates, we will focus on the memories underlying habituation and sensitization in the marine mollusc Tritonia. The basic procedure is to first identify the individual components of a distributed memory through physiological studies and then evaluate their information content by inserting them one at a time into a realistic computer simulation of the neural circuit in which they reside. The project has three specific aims: 1) Construct a simulation of the escape swim neural circuit in its resting state, before it is modified by training; 2) Characterize the distributed sites of circuit modification produced by training; 3) Construct simulations incorporating individual components of the distributed circuit modifications produced by training, and use them to address several issues of information storage. Knowledge of how memory is organized in nervous systems could be of great value in understanding the consequences of brain injury, and in forecasting the consequences of certain surgical procedures. It may also lead to useful design ideas in the area of artificial intelligence.